JP4499131B2 - Manufacturing method of polarizing film - Google Patents

Description

The present invention relates to a method for producing a polarizing film comprising a uniaxially stretched polyvinyl alcohol film, which is useful as a material for a polarizing plate used as a component of a liquid crystal display device.

  A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The application fields of this LCD are also used in small devices such as calculators and wristwatches in the early stages of development, and in recent years, laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, personal phones, and indoors and outdoors. There is a need for a polarizing plate that is widely used in measuring instruments, has less color spots than conventional products, and has a large area.

  In general, a polarizing plate is obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be abbreviated as “PVA” and a polyvinyl alcohol-based film as “PVA film”) and dyeing with iodine or a dichroic dye. Alternatively, after dyeing and uniaxially stretching, a polarizing film obtained by fixing with a boron compound (the dyeing and fixing may be simultaneous) is applied to a cellulose triacetate (TAC) film, acetic acid / A protective film such as a cellulose butyrate (CAB) film is laminated.

By the way, even if it is a PVA film that looks uniform in appearance, the resulting polarizing film may have color spots that are difficult to distinguish from the outside. This color spot is difficult to confirm unless it is a final product (polarizing plate) in which a protective film or the like is laminated. When color spots appear in the final product, a secondary material such as a protective film, which is a good product, is discarded as a defective product, resulting in a large manufacturing loss.
There are roughly two types of color spots. One is large color spots with a pitch of several tens of centimeters in the width direction caused by the influence of neck-in at the time of stretching, and the other is several centimeters in the width direction caused by the influence of film thickness fluctuations. Fine color spots on the pitch. Conventionally, as a method for reducing color spots, studies have been made mainly from the viewpoint of reducing thickness spots and birefringence spots on polyvinyl alcohol films (see Patent Document 1). By reducing the thickness spots and birefringence spots on the polyvinyl alcohol film, it was possible to reduce the fine color spots to some extent to meet the level required at the time, but the final product (polarized light) has improved in recent years. Increasingly, it has been found difficult to reduce the level of color spots that can be problematic in board and liquid crystal display devices.

JP-A-6-138319 (Claims, pages 2-3)

  In addition, with an increase in size of the liquid crystal display device, a polarizing film having a large area has been required. In conventional liquid crystal display devices, since the display area is relatively small and the polarizing plate is used alone, large color spots are unlikely to be a problem, but when the display area is large, the uniformity of the entire display area The problem of color spots has become apparent due to reasons such as being required. In particular, in the case of a polarizing film produced by stretching a polyvinyl alcohol film uniaxially, a difference in optical characteristics between the central portion and the end portion of the film may cause a problem as a large color spot. Therefore, when manufacturing a polarizing film for a large-screen liquid crystal display, there is a problem that the color efficiency is relatively small, for example, since the product is collected only from the central portion, the production efficiency is lowered. .

Accordingly, an object of the present invention is to provide a method for producing a polarizing film that has few color spots and can cope with an increase in the size of a display device incorporating a liquid crystal display and is useful as a material for a polarizing plate used as a component of the liquid crystal display. There is to do.

In order to achieve the above object, the polarizing film of the present invention has a degree of polarization (E) at the center in the width direction of the film and a degree of polarization (F) at a position 50 cm from the center to the width direction of 0.999 ≦ It consists of a uniaxially stretched polyvinyl alcohol film characterized by having a relationship of F / E ≦ 1.001.
The conventional polyvinyl alcohol film used as a material for a polarizing film has been attempted to reduce color spots by improving the uniformity of the film before stretching. For the purpose of improving the uniformity of the degree, the degree of swelling of the film before stretching is adjusted. Normally, when the polyvinyl alcohol film is uniaxially stretched, neck-in occurs, the thickness at the end in the width direction becomes larger than that at the center, and the degree of polarization is different between the end and the center. The present invention improves the degree of polarization of the stretched film by adjusting the degree of swelling in the width direction of the film, thereby causing a more rapid neck-in, and substantially reduces the level of color spots observed visually. It is possible to reduce this.

Since the polarizing film produced by uniaxially stretching the PVA film in the present invention has a small degree of polarization unevenness, the color unevenness due to the degree of polarization is also small, and can be suitably used as a component of a large liquid crystal display device.

In the present invention, the polyvinyl alcohol film used for uniaxial stretching is characterized in that the degree of swelling in the width direction of the film gradually increases toward the end. The degree of swelling (A) at the center in the width direction of the polyvinyl alcohol film and the degree of swelling (C) at a position 100 cm from the center in the width direction have a relationship of 1.08 ≦ C / A ≦ 1.12. Is more preferable, and the relationship of 1.09 ≦ C / A ≦ 1.11 is more preferable. Even if C / A is smaller than 1.08 or larger than 1.12, the change in the degree of polarization in the width direction of the polarizing film obtained by uniaxially stretching the polyvinyl alcohol film becomes large, and color spots are accompanied accordingly. Since it becomes large, it is not preferable.
In the polyvinyl alcohol film used for uniaxial stretching in the present invention, the degree of swelling (A) at the center in the width direction of the film and the degree of swelling (B) at a position 50 cm in the width direction from the center are 1.03 ≦ B. The relationship of /A≦1.07 is more preferable, and the relationship of 1.04 ≦ B / A ≦ 1.06 is more preferable. The effect of reducing the degree of change in the degree of polarization in the width direction is further increased in a polarizing film produced from a polyvinyl alcohol film in which B / A satisfies the above relationship.
Moreover, the polyvinyl alcohol film used for uniaxial stretching in the present invention has a degree of swelling (A) at the center in the width direction of the film and a degree of swelling (D) at a position 150 cm in the width direction from the center. ≦ D / A ≦ 1.17 is more preferable, and 1.14 ≦ D / A ≦ 1.16 is more preferable. A polarizing film produced from a polyvinyl alcohol film having a D / A satisfying the above relationship has an even greater effect of reducing the degree of change in the degree of polarization in the width direction.

  In the present invention, a polarizing film produced by uniaxially stretching a polyvinyl alcohol film has an excellent characteristic that the degree of polarization in the width direction is uniform. That is, in the polarizing film, the degree of polarization (E) at the center in the width direction of the film and the degree of polarization (F) at a position 50 cm in the width direction from the center are 0.999 ≦ F / E ≦ 1.001. More preferably, the relationship of 0.9995 ≦ F / E ≦ 1.0005 can be satisfied.

  The PVA used in the present invention is produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. Further, modified PVA obtained by graft-copolymerizing unsaturated carboxylic acid or derivative thereof, unsaturated sulfonic acid or derivative thereof, α-olefin having 2 to 30 carbon atoms or the like in a proportion of less than 5 mol% on the main chain of PVA, vinyl It is produced by saponifying a modified polyvinyl ester obtained by copolymerizing an ester with an unsaturated carboxylic acid or derivative thereof, an unsaturated sulfonic acid or derivative thereof, an α-olefin having 2 to 30 carbon atoms, or the like at a ratio of less than 15 mol%. Examples thereof include modified PVA and so-called polyvinyl acetal resin obtained by crosslinking a part of hydroxyl groups with aldehydes such as formalin, butyraldehyde, and benzaldehyde.

  Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the like.

  The comonomer used for the modified PVA is copolymerized mainly for the purpose of modifying the PVA, and is used within a range not impairing the gist of the present invention. Examples of such comonomers include olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, acrylic acid Acrylic esters such as n-butyl, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts; methyl methacrylate, methacrylic acid Methacryl such as ethyl, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate Acid Este Acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and its salt, acrylamide propyl dimethylamine and its salt, N-methylol acrylamide and its derivatives, etc. Acrylamide derivatives; methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propane sulfonic acid and its salts, methacrylamide propyl dimethylamine and its salts, N-methylol methacrylamide and its derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether; Vinyl ethers such as til vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride , Vinyl halides such as vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and salts thereof or esters thereof; itaconic acid and salts thereof or esters thereof; vinyltrimethoxysilane And vinyl silyl compounds such as isopropenyl acetate. Among these, α-olefins are preferable, and ethylene is particularly preferable. The modified amount of the modified PVA is preferably less than 15 mol%.

  The saponification degree of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, further preferably 99 mol% or more, and most preferably 99.5 mol% or more from the viewpoint of the polarizing performance and durability of the polarizing film. .

  The saponification degree indicates the proportion of units that are actually saponified to vinyl alcohol units among the units that can be converted to vinyl alcohol units by saponification. The saponification degree of PVA was measured by the method described in JIS.

  The polymerization degree of PVA is preferably 500 or more, more preferably 1000 or more, further preferably 1500 or more, and most preferably 2500 or more from the viewpoint of the polarization performance and durability of the polarizing film. The polymerization degree of PVA is preferably 8000 or less, and more preferably 6000 or less.

  The degree of polymerization of the PVA is measured according to JIS K 6726. That is, it is obtained from the intrinsic viscosity measured in 30 ° C. water after re-saponifying and purifying PVA.

  As a method of producing a PVA film using the above PVA, in addition to a method of forming hydrous PVA by a melt extrusion method, for example, a PVA solution in which PVA is dissolved in a solvent is used, and casting film formation is performed. Method, wet film-forming method (discharge into a poor solvent), gel film-forming method (method of obtaining a PVA film by extracting and removing a solvent after cooling and gelling a PVA aqueous solution once), and a combination of these, etc. Can be adopted. Among these, the casting film forming method and the melt extrusion film forming method are preferable because a good PVA film can be obtained.

In the present invention, as a method for controlling the degree of swelling in the width direction of the PVA film, a method for controlling the temperature of the PVA stock solution in the width direction of the film, a drying temperature or a heat treatment temperature after the PVA stock solution is formed into a film shape with a die or the like. A method for controlling the above can be used.
A preferred method is to gradually increase the heater temperature in the width direction of the die toward the end when manufacturing the PVA film. During the production of the PVA film, the heater temperature (a) at the center in the width direction of the die and the heater temperature (c) at a position 100 cm from the center in the width direction satisfy 1.08 ≦ c / a ≦ 1.12. It is preferable that the relationship is satisfied, and it is more preferable that the relationship is 1.09 ≦ c / a ≦ 1.11. Even if c / a is smaller than 1.08 or larger than 1.12, the change in the degree of polarization in the width direction of the polarizing film obtained by uniaxially stretching the PVA film tends to increase, and the color spots tend to increase. Is seen.
Further, at the time of manufacturing the PVA film, the heater temperature (a) at the center in the width direction of the die and the heater temperature (b) at a position 50 cm in the width direction from the center are 1.03 ≦ b / a ≦ 1.07. More preferably, the relationship is 1.04 ≦ b / a ≦ 1.06. In the polarizing film produced from the PVA film in which b / a satisfies the above relationship, the effect of reducing the degree of change in the degree of polarization in the width direction is further increased.
Further, at the time of manufacturing the PVA film, the heater temperature (a) at the center in the width direction of the die and the degree of swelling (d) at a position 150 cm in the width direction from the center are 1.13 ≦ d / a ≦ 1.17. More preferably, the relationship is 1.14 ≦ d / a ≦ 1.16. A polarizing film produced from a PVA film in which d / a satisfies the above relationship has an even greater effect of reducing the degree of change in the degree of polarization in the width direction.

  Examples of the solvent for dissolving PVA used in producing the PVA film include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Examples thereof include trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, water, and the like, and one or more of these can be used. Among these, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.

  The PVA concentration of the PVA solution or water-containing PVA used when producing the PVA film varies depending on the polymerization degree of the PVA, but is preferably 20 to 70% by weight, more preferably 25 to 60% by weight. 30 to 55% by weight is more preferred, and 35 to 50% by weight is most preferred. When the PVA concentration is higher than 70% by weight, the viscosity of the PVA solution or the hydrous PVA becomes too high to make filtration and defoaming difficult, and it becomes difficult to obtain a film free from foreign matters and defects. On the other hand, when the PVA concentration is lower than 20% by weight, the viscosity of the PVA solution or the hydrous PVA becomes too low, and it becomes difficult to produce a PVA film having a target thickness. Further, the PVA solution or the hydrous PVA may contain a plasticizer, a surfactant, a dichroic dye or the like as necessary.

  When producing the PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc., and one or more of these are used. can do. Among these, diglycerin, ethylene glycol, or glycerin is preferably used in terms of the effect of improving stretchability.

  The addition amount of the polyhydric alcohol is preferably 1 to 30 parts by weight, more preferably 3 to 25 parts by weight, and most preferably 5 to 20 parts by weight with respect to 100 parts by weight of PVA. If the amount of polyhydric alcohol added is less than 1 part by weight, the dyeability and stretchability of the PVA film may be reduced, and if it is more than 30 parts by weight, the PVA film becomes too flexible and the handleability decreases. There is a case.

  When producing a PVA film, it is preferable to add a surfactant. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable. As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzene sulfonate are suitable. Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkylphenyl ether types such as polyoxyethylene octylphenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene laurylamino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether, etc. Nonionic surfactants such as allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.

  The addition amount of the surfactant is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.5 part by weight, and most preferably 0.05 to 0.3 part by weight with respect to 100 parts by weight of PVA. . When the addition amount of the surfactant is less than 0.01 parts by weight, the effect of improving the film forming property and the peelability due to the addition of the surfactant is difficult to appear, and when it is more than 1 part by weight, the surfactant is a PVA film. It may elute on the surface of the glass and cause blocking, which may reduce the handleability.

  In the present invention, the thickness of the polyvinyl alcohol film is preferably 10 to 100 μm, and more preferably 20 to 80 μm. When the thickness of the PVA film is less than 10 μm, the film strength is too low to perform uniform stretching and color spots are likely to occur. When the thickness of the PVA film exceeds 100 μm, when a polarizing film is produced by uniaxially stretching the PVA film, a thickness change due to neck-in at the end portion is likely to occur, and color spots are easily emphasized, which is not preferable.

  In order to produce a polarizing film from a PVA film, for example, the PVA film may be dyed, uniaxially stretched, fixed, dried, and further heat treated as necessary. There are no particular restrictions. Moreover, you may perform uniaxial stretching twice or more.

  Dyeing can be performed at any operation stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. As dyes used for dyeing, iodine-potassium iodide; direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81 , 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Dichroic dyes such as yellow 8, 12, 44, 86, 87; direct orange 26, 39, 106, 107 can be used in one kind or a mixture of two or more kinds. The normal dyeing is generally performed by immersing the PVA film in a solution containing the dye, but the processing conditions and processing method are not particularly limited, such as mixing with the PVA film to form a film.

  For uniaxial stretching, a wet stretching method in which a PVA film is stretched in a warm aqueous solution such as a boric acid aqueous solution (in a solution containing the dye or in a fixed treatment bath described later), or a PVA film after being hydrated in air. A dry heat stretching method of stretching can be used. The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched (wet stretching) in warm water, and 50 to 180 ° C. when it is dry heat stretched. Further, the stretching ratio of uniaxial stretching (in the case of performing uniaxial stretching in multiple stages) is preferably 4 times or more, particularly preferably 5 times or more from the viewpoint of polarization performance. Although there is no upper limit in the strict sense about the draw ratio, it is preferable that the draw ratio is 8 times or less because uniform stretching can be easily obtained. The thickness of the film after stretching is preferably from 3 to 75 μm, more preferably from 5 to 50 μm.

  Fixing treatment is often performed for the purpose of strengthening the adsorption of the dye to the PVA film. Usually, boric acid and / or boron compounds are added to the treatment bath used for the fixing treatment. Moreover, you may add an iodine compound in a processing bath as needed.

  It is preferable to perform the drying process of the obtained polarizing film at 30-150 degreeC, and it is more preferable to carry out at 50-150 degreeC.

  The polarizing film obtained as described above is usually used as a polarizing plate by attaching a protective film optically transparent and having mechanical strength on both sides or one side. As the protective film, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive for bonding the polarizing film and the protective film include PVA-based adhesives and urethane-based adhesives, among which PVA-based adhesives are suitable.

  The polarizing plate obtained as described above is used as a part of a liquid crystal display device after being coated with an acrylic adhesive or the like and then bonded to a glass substrate. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, or the like may be bonded simultaneously.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In Examples and Comparative Examples, the degree of swelling of the polyvinyl alcohol film and the transmittance of the polarizing film were measured by the following methods.

Swelling degree of polyvinyl alcohol film:
About 2 g of polyvinyl alcohol film is collected and cut into a width of about 2 mm. After being immersed in distilled water at 30 ° C. for 10 minutes, centrifugal dehydration was performed, and the wet weight was measured. Furthermore, drying was performed at 105 ° C. for 24 hours, and the dry weight was measured.
Then, the degree of swelling was determined by the formula [wet weight] ÷ [dry weight] × 100.

Transmittance of polarizing film:
Using a spectrophotometer UV-2200 (attached to an integrating sphere) manufactured by Shimadzu Corporation, a Y value after correcting the visibility in the visible light region of the C light source and the 2-degree visual field is measured on a polarizing film sample of about 4 × 4 cm, The transmittance was determined from the average values in the 45 ° and −45 ° directions with respect to the stretching axis direction of the polarizing film.

Example 1
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion from a T die to a metal roll was performed. Filmed. At this time, the heater temperature in the width direction of the T die was set to 100 ° C., 105 ° C., 110 ° C., and 115 ° C. at intervals of 50 cm from the center in the width direction toward the end. The film was dried and heat-treated to obtain a PVA film having a width of 3 m. The thickness of the obtained PVA film was 50 μm. The swelling degree of the film was 160%, 168%, 176%, and 182% every 50 cm from the center in the width direction toward the end. The ratio of the degree of swelling (A) at the center in the width direction of the film to the degree of swelling (C) at a position 100 cm from the center to the width was 1.10.

  The PVA film was continuously treated in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to prepare a polarizing film. That is, the PVA film was immersed in 30 ° C. water for 30 seconds to be pre-swelled, and then immersed in an aqueous solution having an iodine concentration of 0.6 g / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%, in a 30 ° C. aqueous solution with a potassium iodide concentration of 40 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.

  The width of the obtained polarizing film is 1.5 m, the degree of polarization (E) at the center in the width direction is 99.93%, and the degree of polarization (F) at a position 50 cm from the center in the width direction is 99.89. % And F / E was 0.9996. When the polarizing film was placed at an angle of 90 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the center part and the end part with respect to the width direction of the obtained polarizing film The difference in brightness was small, and the color spots were small and good.

Example 2
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion from a T die to a metal roll was performed. Filmed. At this time, the heater temperature in the width direction of the T-die was set to 85 ° C., 89 ° C., 94 ° C., and 98 ° C. every 50 cm from the center in the width direction toward the end. The film was dried and heat-treated to obtain a PVA film having a width of 3 m. The thickness of the obtained PVA film was 50 μm. The degree of swelling of the film was 175%, 181%, 189%, and 198% every 50 cm from the center in the width direction toward the end. The ratio of the degree of swelling (A) at the center in the width direction of the film to the degree of swelling (C) at a position 100 cm from the center in the width direction was 1.08.

  The PVA film was continuously treated in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to prepare a polarizing film. That is, the PVA film was immersed in 30 ° C. water for 30 seconds to be pre-swelled, and then immersed in an aqueous solution having an iodine concentration of 0.7 g / liter and a potassium iodide concentration of 60 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%, in a 30 ° C. aqueous solution with a potassium iodide concentration of 50 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.

  The width of the obtained polarizing film is 1.5 m, the degree of polarization (E) at the center in the width direction is 99.95%, and the degree of polarization (F) at a position 50 cm from the center in the width direction is 99.98. % And F / E was 1.0003. When the polarizing film was placed at an angle of 90 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the center part and the end part with respect to the width direction of the obtained polarizing film The difference in brightness was small, and the color spots were small and good.

Comparative Example 1
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water. Filmed. At this time, the heater temperature in the width direction of the T die was set to 90 ° C., 95 ° C., 95 ° C., and 95 ° C. every 50 cm from the center portion in the width direction toward the end portion. The film was dried and heat-treated to obtain a PVA film having a width of 3 m. The thickness of the obtained PVA film was 50 μm. The degree of swelling of the film was 170%, 175%, 175%, and 175% every 50 cm from the center to the end in the width direction. The ratio of the degree of swelling (A) at the center in the width direction of the film to the degree of swelling (C) at a position 100 cm from the center in the width direction was 1.03.

  The PVA film was continuously treated in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to prepare a polarizing film. That is, the PVA film was immersed in 30 ° C. water for 30 seconds to be pre-swelled, and then immersed in an aqueous solution having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%, in a 30 ° C. aqueous solution with a potassium iodide concentration of 40 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.

  The width of the obtained polarizing film is 1.5 m, the degree of polarization (E) at the center in the width direction is 99.89%, and the degree of polarization (F) at a position 50 cm from the center in the width direction is 99.91. % And F / E was 1.0002. When the polarizing film was placed at an angle of 90 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the center part and the end part with respect to the width direction of the obtained polarizing film The difference in brightness was large, and the color spots were large, which was unsatisfactory as a polarizing film for large liquid crystal displays.

Comparative Example 2
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion from a T die to a metal roll was performed. Filmed. At this time, the heater temperature in the width direction of the T die was set to 90 ° C., 105 ° C., 105 ° C., and 105 ° C. at intervals of 50 cm from the center in the width direction toward the end. The film was dried and heat-treated to obtain a PVA film having a width of 3 m. The thickness of the obtained PVA film was 50 μm. The degree of swelling of the film was 170%, 196%, 196%, and 196% every 50 cm from the center to the edge in the width direction. The ratio of the degree of swelling (A) at the center in the width direction of the film to the degree of swelling (C) at a position 100 cm from the center in the width direction was 1.15.

  The PVA film was continuously treated in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to prepare a polarizing film. That is, the PVA film was immersed in 30 ° C. water for 30 seconds to be pre-swelled, and then immersed in an aqueous solution having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%, in a 30 ° C. aqueous solution with a potassium iodide concentration of 40 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.

  The width of the obtained polarizing film is 1.5 m, the degree of polarization (E) at the center in the width direction is 99.89%, and the transmittance (F) at a position 50 cm from the center in the width direction is 99.99. % And F / E was 1.001. When the polarizing film was placed at an angle of 90 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the center part and the end part with respect to the width direction of the obtained polarizing film The difference in luminance between them was large and the color spots were also large, which was unsatisfactory as a polarizing film for large liquid crystal displays.

Since the polarizing film produced by uniaxially stretching the PVA film in the present invention has a small degree of polarization unevenness, the color unevenness due to the degree of polarization is also small, and can be suitably used as a component of a large liquid crystal display device.

Claims (3)

Polyvinyl alcohol film in which the degree of swelling (A) at the center of the film in the width direction and the degree of swelling (C) at a position 100 cm from the center in the width direction have a relationship of 1.08 ≦ C / A ≦ 1.12. The degree of polarization (E) at the center portion in the width direction of the film and the degree of polarization (F) at a position 50 cm from the center portion in the width direction are characterized in that 0.999 ≦ F / E ≦ A method for producing a polarizing film having a relationship of 1.001 . The degree of swelling (A) at the center in the width direction of the polyvinyl alcohol film and the degree of swelling (B) at a position 50 cm from the center in the width direction are in a relationship of 1.03 ≦ B / A ≦ 1.07. Item 10. A method for producing a polarizing film according to Item 1 . The degree of swelling (A) at the center in the width direction of the polyvinyl alcohol film and the degree of swelling (D) at a position 150 cm from the center in the width direction are in a relationship of 1.13 ≦ D / A ≦ 1.17. Item 3. A method for producing a polarizing film according to Item 1 or 2 .